Five metabolites (1-5), including two new sesquiterpenoids, designated ganodermanol L (1) and 4α,15-epoxyeudesmane-1β,6α,11-triol (2), together with three known structurally related compounds (3-5), have been isolated from the cultures of Streptomyces sp. XM17, a bacteria residing in the fresh feces of the giant panda Ailuropoda melanoleuca. The structures of 1-2 were established on the basis of extensive spectroscopic analyses, including 1D- and 2D-NMR (1H-1H COSY, HMQC, HMBC and NOESY) experiments. Furthermore, the absolute configuration of 1 was established by single-crystal X-ray crystallographic analyses. Of noted, these compounds were found to possessed antiviral activities using the 'pretreatment of virus' approach with IC50 values ranging from 4 to 30 nM, indicating that these sesquiterpenoids were potent in inhibiting the entry of influenza A virus.
Keywords: Ailuropoda melanoleuca; Sesquiterpenoids; Streptomyces sp; antiviral activity; natural product.